A Long Cycle‐Life High‐Voltage Spinel Lithium‐Ion Battery Electrode Achieved by Site‐Selective Doping

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode candidate for the next‐generation high energy‐density lithium‐ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site‐selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fd m structure. This site‐selective doping not only suppresses unfavorable two‐phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg‐doped LNMOs exhibit extraordinarily stable electrochemical performance in both half‐cells and prototype full‐batteries with novel TiNb₂O₇ counter‐electrodes. This work pioneers an atomic‐doping engineering strategy for electrode materials that could be extended to other energy materials to create high‐performance devices.     

Review on gel polymer electrolytes for lithium batteries

This paper reviews the state-of-art of polymer electrolytes in view of their electrochemical and physical properties for the applications in lithium batteries. This review mainly encompasses on five polymer hosts namely poly(ethylene oxide) (PEO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF) and poly(vinylidene fluoride-hexafluoro propylene) (PVdF-HFP) as electrolytes. Also the ionic conductivity, morphology, porosity and cycling behavior of PVdF-HFP membranes prepared by phase inversion technique with different non-solvents have been presented. The cycling behavior of LiMn₂O₄/polymer electrolyte (PE)/Li cells is also described.     

Enhancing the Electrochemical Performance of a High-Voltage LiNi0.5Mn1.5O4 Cathode in a Carbonate-Based Electrolyte with a Novel and Low-Cost Functional Additive

Butyric anhydride (BA) is used as an effective functional additive to improve the electrochemical performance of a high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode. In the presence of 0.5 wt % BA, the capacity retention of a LNMO/Li cell is significantly improved from 15.3 to 88.4 % after 200 cycles at 1 C. Furthermore, the rate performance of the LNMO/Li cell is also effectively enhanced, and the capacity goes up to 112 mAh g⁻¹ even at 5 C, which is considerably higher than that of a LNMO/Li cell in electrolyte without BA additive (95.4 mAh g⁻¹ at 5 C). Linear sweep voltammetry and cyclic voltammetry results reveal that the BA additive can be preferentially oxidized to construct a stable cathode electrolyte interphase (CEI) film on the LNMO cathode. Subsequently, the BA-derived CEI film can alleviate the decomposition of the electrolyte and the dissolution of Mn and Ni ions from the LNMO cathode as well as maintain the structural stability of LNMO during the cycling process; this leads to outstanding electrochemical performance. Thus, this work provides an effective and low-cost functional electrolyte for high-voltage LNMO-based LIBs.     

A Long Cycle-Life High-Voltage Spinel Lithium-Ion Battery Electrode Achieved by Site-Selective Doping

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode candidate for the next-generation high energy-density lithium-ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site-selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fd m structure. This site-selective doping not only suppresses unfavorable two-phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg-doped LNMOs exhibit extraordinarily stable electrochemical performance in both half-cells and prototype full-batteries with novel TiNb₂O₇ counter-electrodes. This work pioneers an atomic-doping engineering strategy for electrode materials that could be extended to other energy materials to create high-performance devices.     

Spinel LiNi0.5Mn1.5O4 with ultra-thin Al2O3 coating for Li-ion batteries: investigation of improved cycling performance at elevated temperature

In this study, spinel LiNi_0.5Mn_1.5O₄ (LNMO) was successfully decorated with Al₂O₃ thin film by using atomic layer deposition (ALD) approach and evaluated as a cathode material for high-temperature applications in lithium ion batteries (LIBs). To optimize the LNMO-Al₂O₃ electrodes operated at elevated temperature (55 °C), the effects of Al₂O₃ thicknesses adjusted by controlling the ALD deposition cycle were systemically investigated. According to the series of electrochemical results, the LNMO coated with the Al₂O₃ thin layer in the thickness of ca. 2 nm was achieved by using one-cycle ALD and the LNMO-Al₂O₃ electrode exhibited superior electrochemical stability (capacity retention up to 93.7% after consecutive 150 charge/discharge cycles at 0.5 C to the pristine LNMO electrode at elevated temperature. This can be attributed to two factors: (i) the decoration of Al₂O₃ thin layer could not contribute remarkably to extra resistance for charge transfer; (ii) Al₂O₃ thin film deposition could efficiently stabilize the growth of cathode electrolyte interface (CEI) and suppress the dissolution of transition metals. Therefore, these results verify that the LNMO-Al₂O₃ electrode could be regarded as a promising cathode material for high-voltage LIBs, especially at elevated temperature operation.

     

Instability of PVDF Binder in the LiFePO4 versus Li4Ti5O12 Li-Ion Battery Cell

The conventional formulation of electrodes used in Li-ion batteries consists of a mixture of three components: an active material, a conductive additive (carbon), and an organic binder. While the first encompasses a broad spectrum of chemistries, the carbon and the binder are often standard elements of the composite, with the latter being, in most of the cathode cases, the polyvinylidene fluoride (PVDF). The high (electro-)chemical inertia spanning over a broad range of oxidative and reductive potentials gives grounds for this choice. Herein, we demonstrate, contrary to electrochemical expectations, that the PVDF is electrochemically unstable at relatively low potentials. We consider in this study the LiFePO₄ (LFP) cathode cycled versus Li₄Ti₅O₁₂ (LTO) anode as a representative low-voltage battery cell system. The binder degradation process starts upon charge on the LFP electrode at 3.45 V vs. Li⁺/Li when the PVDF binder reacts with lithium and forms LiF. The latter does not precipitate on the LFP but migrates/diffuses towards the LTO counter-electrode, following the Li-ions’ trajectory. X-Ray photoelectron spectroscopy complemented with the high lateral resolution of X-ray photoemission electron microscopy disclosed the formation of a thin layer of LiF homogenously distributed across the LTO electrode, which partially dissolves (or decomposes) upon discharge. The degradation of the PVDF and the deposition and dissolution (and/or decomposition) of the LiF layer continue over subsequent charge and discharge cycles. The process is augmented when the cycling temperature is increased to 80 °C. The results shown in this work are crucial to interpret electrochemical data, such as specific charge decay or impedance rise, and have relevance for all PVDF-based electrodes, especially when employed in high-voltage battery cells where the more extreme cycling conditions exacerbate electrode components’ stability.     

SEI layer-forming additives for LiNi0.5Mn1.5O4/graphite 5 V Li-ion batteries

This study demonstrates that proper SEI layer on graphite anode is essential in LiNi_0.5Mn_1.5O₄(LNMO)/graphite 5 V lithium-ion batteries. Succinic anhydride (SA) and 1,3-propane sultone (PS) were found to greatly extend cycle life and suppress swelling behavior of LNMO/graphite cells. The benefits of SA and PS were ascribed not only to the stable SEI layer they form on graphite but also to their stability toward the oxidation at high voltage. Using 1 M LiPF₆ EC/EMC (1/2, v/v) solutions with SA and PS, LNMO/graphite Al-laminated pouch cell with nominal capacity of 600 mA h exhibited about 80% capacity retention after 100 cycles. This is the first report on the successful LNMO/graphite 5 V LIB to our best knowledge.     

Elucidating the function of modified carbon blacks in high-voltage lithium-ion batteries: impact on electrolyte decomposition

We report on the improved electrochemical performance of a high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode using surface-modified carbon blacks (CBs) as conductive agents. Facile modifications of CBs were achieved using thermal, urea-based hydrothermal, and acid oxidation treatments. The material properties of the modified CBs, LNMO-based electrode surface, and electrolyte compositions were investigated and correlated. Based on the distribution of the decomposition deposits on the surface of the electrode, it is confirmed that CB, rather than the LNMO active material, dominates the electrolyte decomposition site at a high voltage, owing to its relatively high surface area for the reaction. Additionally, compared with the pristine CB, the hydrothermally treated N-doped CB (HCB) improves the electrochemical performance of the LNMO cathode, although the thermally treated sample exhibits the most adverse influence, followed by the oxidized one. The LNMO/HCB cathode attains optimum capacity retention (approximately 95%) for 100 cycles (1 C) and a high rate capability (70%, 5 C/0.2 C), corresponding to a lowered resistance at the cathode–electrolyte interface. Furthermore, HCB with a limited specific surface area and increased defects, as well as additional pyrrolic-N and pyridinic-N groups, substantially reduces the decomposition deposits on the surface of the electrode and the decomposition products in the electrolyte. These phenomena account for the improved electrochemical performance of the LNMO/HCB cathode.     

Cu3P纳米板阵列@泡沫铜三维骨架的原位构筑及其作为高性能锂金属负极

通过简单的原位生长法,将Cu3P纳米板阵列均匀负载在商业化的泡沫铜内部(NF?Cu3P@Cu),并用作锂金属负极的三维骨架载体材料。亲锂性的Cu3P纳米板阵列可以提供均匀且丰富的锂成核活性位点,诱导锂金属在NF?Cu3P@Cu内快速形核和均匀电沉积。同时,在电镀沉积锂时,Cu3P纳米板阵列会被锂化形成快离子导体Li3P,可以确保锂离子在复合负极中的快速均匀传输,从而有效抑制锂枝晶的形成。因此,获得的Li@NF?Cu3P@Cu复合负极材料在对称电池和全电池中,均表现出优异的循环稳定性。     

The effect of nanolayer AlF<Subscript>3</Subscript> coating on LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cycle life in high temperature for lithium secondary batteries

The surface of the spinel LiMn₂O₄ was coated with AlF₃ by a chemical process to improve its electrochemical performance at high temperatures. The morphology and structure of the original and AlF₃-coated LiMn₂O₄ samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. It was found that the surfaces of the original LiMn₂O₄ samples were covered with a nanolayer AlF₃ after the treatment. The charge/discharge of the materials were carried at 220 mA/g in the range of 3.0 and 4.4 V at 55°C. While the original LiMn₂O₄ showed 17.8% capacity loss in 50 cycles at 55°C, the AlF₃-coated LiMn₂O₄ (118.1 mA h/g) showed only 3.4% loss of the initial capacity (122.3 mA h/g) at 55°C. It is obvious that the improvement in cycling performance of the coated-LiMn₂O₄ electrode at 55°C is attributed to the presence of AlF₃ on the surface of LiMn₂O₄. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 817–819. The article is published in the original     

High-performance pyrrolidinium-based poly(ionic liquid) binders for Li-ion and Li-air batteries

The role of binders is crucial to achieve high performance and long cycle lifes in next-generation electrodes for lithium batteries. Currently used binders in electrode configurations, such as poly(vinylidene difluoride) (PVDF) are inactive polymers that do not transport lithium ions themselves, causing restrictions for high-power applications. Thus, developing innovative binders with an affinity towards lithium mobility is important for both lithium-ion and lithium-air batteries. In this work, we present for the first time the use of PDADMA poly(ionic liquid)s with fluorinated anions (FSI, TFSI, BETI, and CFSO) as cathode binders in Li-ion and Li-air batteries. The high-voltage NMC 532 cathodes with fluorinated PDADMA binders showed improved cells performances as: capacity values, rate performance, and cycling stability in accelerating aging conditions dedicated for more environmental-friendly mobility applications. Especially, PDADMA-CFSO binder in cathodes shows a cell capacity increase of 26% at 5C (12 min charge), when compared to PVDF one. Moreover, the fluorinated PDADMA binders in cathode improve the discharge capacities in Li–O₂ cells, both with liquid and solid gel polymer electrolytes. Impressively, the Coulombic efficiency improves by 146% and the cycling capacity by 70% in solid-state Li–O₂ cells using PDADMA-CFSO binder in the cathode, instead of common lithiated Nafion. All in all, the proposed fluorinated PDADMA Poly(ionic liquid)s can be a highly competitive alternative to conventional binders used nowadays in Li-ion and Li-air batteries.     

Effect of Lithia and Substrate on the Electrochemical Performance of a Lithia/Cobalt Oxide Composite Thin‐Film Anode

Highly porous reticular Li₂O/CoO composite thin films fabricated by electrostatic spray deposition were investigated by using X-ray diffraction, scanning electron microscopy, galvanostatic cell-cycling measurements, and AC impedance spectroscopy measurements. The results of the electrochemical tests indicate that the initial coulombic efficiency and capacity retention are dependent on Li₂O content and the specific surface area of the deposited layer. Irrespective of the type of substrate, the electrode gave the best electrochemical performance when the molar ratio of Li to Co was controlled at 1:1. At the optimal composition, at 0.2 C the initial coulombic efficiency was as high as 81.9 % and 83.6 % for the film on Cu foil and on porous Ni, respectively. The Li₂O/CoO (Li/Co=1:1) films on Ni foam and Cu foil had sustained capacities of up to 790 and 715 mAh g⁻¹, respectively, at a rate of 1 C over 100 cycles at 25 °C. Similar cycling experiments carried out at 70 °C showed that the capacity is temperature-sensitive, and it exhibited reversible capacities as high as 1018 (Cu foil) and 1269 mAh g⁻¹ (Ni foam) for up to 100 cycles. The thin-film electrodes on Ni foam always performed better than those on Cu foil. Cycling at elevated temperature (70 °C) also resulted in a significant increase in capacity.     

Ultraviolet-Cured Semi-Interpenetrating Network Polymer Electrolytes for High-Performance Quasi-Solid-State Lithium Metal Batteries

Solid polymer electrolytes with relatively low ionic conductivity at room temperature and poor mechanical strength greatly restrict their practical applications. Herein, we design semi-interpenetrating network polymer (SNP) electrolyte composed of an ultraviolet-crosslinked polymer network (ethoxylated trimethylolpropane triacrylate), linear polymer chains (polyvinylidene fluoride-co-hexafluoropropylene) and lithium salt solution to satisfy the demand of high ionic conductivity, good mechanical flexibility, and electrochemical stability for lithium metal batteries. The semi-interpenetrating network has a pivotal effect in improving chain relaxation, facilitating the local segmental motion of polymer chains and reducing the polymer crystallinity. Thanks to these advantages, the SNP electrolyte shows a high ionic conductivity (1.12 mS cm⁻¹ at 30 °C), wide electrochemical stability window (4.6 V vs. Li⁺/Li), good bendability and shape versatility. The promoted ion transport combined with suppressed impedance growth during cycling contribute to good cell performance. The assembled quasi-solid-state lithium metal batteries (LiFePO₄/SNP/Li) exhibit good cycling stability and rate capability at room temperature.     

Chemical and electrochemical doping in poly(paraphenylene vinylene) blends

Blends of poly(p-phenylene vinylene) (PPV), with other polymers were made by film-casting from an aqueous mixture of the water-soluble sulfonium salt precursor to PPV and the second polymer. The rates of chemical doping, using As F₅, and of electrochemical doping, using perchlorate counter ion, of the PPV component are strongly influenced by the nature of the added macromolecule. In all cases studied the blends appear to be phase separated under all conditions. The most versatile blend was with poly(ethylene oxide) (PEO), which could be heated to 225°C without degradation and which yielded the highest electrical conductivity when doped. The utility of blends was demonstrated using free-standing PPV/PEO blend samples as rechargeable battery electrodes.     

Core‐Shell Structured Cobalt Sulfide/Cobalt Aluminum Hydroxide Nanosheet Arrays for Pseudocapacitor Application

The direct synthesis of nanostructured electrode materials on three‐dimensional substrates is important for their practical application in electrochemical cells without requiring the use of organic additives or binders. In this study, we present a simple two‐step process to synthesize a stable core–shell structured cobalt sulfide/cobalt aluminum hydroxide nanosheet (LDH‐S) for pseudocapacitor electrode application. The cobalt aluminum layered double hydroxide (CoAl‐LDH) nanoplates were synthesized in basic aqueous solution with a kinetically‐controlled thickness. Owing to the facile diffusion of electrolytes through the nanoplates, thin CoAl‐LDH nanoplates have higher specific capacitance values than thick nanoplates. The as‐grown CoAl‐LDH nanoplates were transformed into core–shell structured LDH‐S nanosheets by a surface modification process in Na₂S aqueous solution. The chemically robust cobalt sulfide (CoS) shell increased the electrochemical stability compared to the sulfide‐free CoAl‐LDH electrodes. The LDH‐S electrodes exhibited high electrochemical performance in terms of specific capacitance and rate capability with a galvanostatic discharge of 1503 F g^?1 at a current density of 2 A g^?1 and a specific capacitance of 91 % at 50 A g^?1.     

Electrochemical performance of nano-sized ZnO-coated LiNi0.5Mn1.5O4 spinel as 5 V materials at elevated temperatures

ZnO-coated LiNi_0.5Mn_1.5O₄ powders with excellent electrochemical cyclability and structural stability have been synthesized. The electrochemical performance and structural stability of ZnO-coated LiNi_0.5Mn_1.5O₄ electrodes in the 5 V region at elevated temperature has been studied as function of the level of ZnO coating. The 1.5 wt% ZnO-coated LiNi_0.5Mn_1.5O₄ electrode delivers an initial discharge capacity of 137 mAh g⁻¹ with excellent cyclability at elevated temperature even at 55 °C. The reason for the excellent cycling performance of ZnO-coated LiNi_0.5Mn_1.5O₄ electrode is largely attributed to ZnO playing an important role of HF getting in the electrolyte.     

A Long‐Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution

In this paper, we report an advanced long‐life lithium ion battery, employing a Pyr₁₄TFSI‐LiTFSI non‐flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn‐C) nanocomposite anode, and a layered LiNi_1/3Co_1/3Mn_1/3O₂ (NMC) cathode. The IL‐based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel–Tammann–Fulcher (VTF) trend. Lithium half‐cells employing the Sn‐C anode and NMC cathode in the Pyr₁₄TFSI‐LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn‐C electrodes are combined into a cathode‐limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g^?1 and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL‐based lithium ion cells are suitable batteries for application in electric vehicles.     

Regulating Lithium Plating and Stripping by Using Vertically Aligned Graphene/CNT Channels Decorated with ZnO Particles

Lithium (Li) metal is regarded as the ultimate anode material for use in Li batteries due to its high theoretical capacity (3860 mA h g⁻¹). However, the Li dendrites that are generated during iterative Li plating/stripping cycles cause poor cycling stability and even present safety risks, and thus severely handicap the commercial utility of Li metal anodes. Herein, we describe a graphene and carbon nanotube (CNT)-based Li host material that features vertically aligned channels with attached ZnO particles (designated ZnO@G-CNT-C) and show that the material effectively regulates Li plating and stripping. ZnO@G-CNT-C is prepared from an aqueous suspension of Zn(OAc)₂, CNTs, and graphene oxide by using ice to template channel growth. ZnO@G-CNT-C was found to be mechanically robust and capable of guiding Li deposition on the inner walls of the channels without the formation of Li dendrites. When used as an electrode, the material exhibits relatively low polarization for Li plating, fast Li-ion diffusion, and high Coulombic efficiency, even over hundreds of Li plating/stripping cycles. Moreover, full cells prepared with ZnO@G-CNT-C as Li host and LiFePO₄ as cathode exhibit outstanding performance in terms of specific capacity (155.9 mA h g⁻¹ at 0.5 C), rate performance (91.8 mA h g⁻¹ at 4 C), cycling stability (109.4 mA h g⁻¹ at 0.5 C after 800 cycles). The methodology described can be readily adapted to enable the use of carbon-based electrodes with well-defined channels in a wide range of contemporary applications that pertain to energy storage and delivery.     

New doped Li-M-Mn-O (M = Al, Fe, Ni) spinels as cathodes for rechargeable 3 V lithium batteries

The electrochemical behaviour of new doped Li-M-Mn-O (M = Al, Fe, Ni) spinel oxides in liquid electrolyte lithium cells was studied. The insertion electrode materials were obtained by heating stoichiometric amounts of thoroughly mixed LiOH and M _x Mn_{1− x} CO₃ (M = Fe, Ni; x = 0.08−0.15) or Al _x Mn_{1− x} (CO₃) (OH) _y , in the case of Al, at 380 °C in air for 20 h. The transition metal-doped samples, particularly those containing Ni or obtained at low temperatures, where the resulting spinel was cation-deficient and highly disordered, exhibited the best cycling performance in the potential window 3.3−2.3 V. Cell capacity was retained by 80% after 200 cycles. Capacity fading was observed on increasing the firing temperature, together with improved crystallinity and the disappearance of cation vacancies. This impaired electrochemical behaviour is ascribed to a Jahn-Teller effect, which induces an X-ray-detectable cubic-tetragonal phase transition upon lithium insertion. The phase transition was undetectable in the low-temperature samples. The influence of the Jahn-Teller distortion is thus seemingly lessened by a highly disordered structure. Received: 25 November 1997 / Accepted: 28 January 1998     

锂离子电池正极材料LiV3O8-xClx的低温固相法合成及电化学性能研究

采用低温固相法成功地合成了锂离子电池正极材料LiV3O8-xClx (x=0.00,0.05,0.10,0.15)。分别用XRD、SEM、充放电实验、循环伏安、交流阻抗等测试方法研究了Cl- 的掺入对LiV3O8结构、形貌及电化学性能的影响。结果表明, Cl-的掺入显著地提高了材料的充放电循环性能。当掺杂量 x=0.10时,材料的循环性能最好, 循环100周后放电容量仍为198.6 mAh/g。